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Old March 10th 19, 09:38 PM posted to rec.bicycles.tech
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Default GPS Units = Show road steepness?

On Sunday, March 10, 2019 at 11:11:41 AM UTC-7, Bertrand wrote:
On 3/10/2019 10:56 AM, Mark J. wrote:
On 3/9/2019 4:46 PM, Sir Ridesalot wrote:
Talking about GPS units on another thread reminded me of something else I
wondered if they do. Does a bicycle GPS unit show you the steepness of roads?
There's an area that I frequently ride where on road has short but very steep
hills, another road a mile or so east of it has much more gradual hills whilst
a third road to the west of the first one is a major highway that can be
ridden with a bicycle. What I'm wondering is this: if someone unfamiliar with
the area got there and used a GPS unit to show those three roads, would the
GPS unit show them the different gradients of the roads? Or is that another
function that they'd need to download or otherwise install?

Cheers

As others have noted, many (all?) Garmin units can display gradient (as in "6%
grade".Â* As noted in another thread, GPS units are notoriously not very accurate
in their altitude calculation, so the more expensive units have a barometric
"backup".Â* If you are using a pre-loaded course (e.g. a .TCX file) on your GPS,
(?some? ?all? my!) Garmins can display the profile of the upcoming few miles.

My own experience over 7 years with Garmin units (that have barometric "backup"
to the altimeter calculation) is that the reported gradient is /fairly/
consistently reported (on many rides over the same hills), though the peak
steepness will vary by a percent or so.Â* Maybe that's 'cause I wasn't looking
when the highest number was on the screen, or because the unit updated at
different points on the road on different rides of the hill.

Finally, if you use ridewithgps.com, and I assume any similar sites/software,
note that gradient reporting there usually misses peak values, as the software
tends to average over larger segments of the course.Â* For example, on one local
hill I ride a lot, the peak gradient appears to be about 12% for maybe 50-100
feet, as measured with both GPS and inclinometer.Â* Ridewithgps.com reports a
peak of 7.2%, which is probably true if you average over longer segments.

Mark J.


Here's an article on the trickiness of measuring steepness:

http://www.roberts-1.com/b/v/e/08a/i...ring_steepness


Since the usual GPS satellites are well over the horizon, using them to get an accurate altitude reading is difficult at the very least. Also the news ones are pretty low altitude and moving really fast. This compounds the problem.

So there has to be one hell of a lot of computation just to find your position let alone your altitude. Now let's make it more complicated - the MPU's use more energy the faster they operate so if you want your unit to last a long time and be reasonably compact AND do all of this computation you really have your hands full with just position let alone attempting to calculate altitude.

The way I would first look into it would be to use a satellite as close to zenith as possible and use signal transit time to calculate altitude.

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